An electrical signal can degrade as it is transmitted via a medium, such as a cable or trace on a circuit board. For example, a signal's frequency spectrum can be changed, such as including attenuation of high-frequency components of the transmitted signal. In a digital signal, narrow signal pulses can exhibit lower peak amplitudes than wide pulses, which can lead to errors in bit recovery. Another result of frequency spectrum degradation is signal “jitter,” that is, signal transitions that may not occur at multiples of a fixed time interval. It can be difficult to recover data from a signal that exhibits greater than a threshold amount of jitter.
In an example, a data signal can be equalized or filtered to compensate for frequency degradation, such as to restore various attenuated frequency components of the original signal. In some examples, characteristics of a transmission medium and/or of a transmitted signal itself, such as a frequency or data rate, can vary. For example, a cable length can vary significantly, such as from zero to 100 meters in the case of a 100BASE-TX Ethernet network. Different equalization settings can be thus be used depending on the circumstances of a particular signal or channel. For example, signals transmitted over relatively short cable lengths will generally benefit from different equalization than signals transmitted over longer cable lengths.
An adaptive or adjustable equalizer circuit can be configured to provide different amounts of types of signal equalization or signal processing to an input signal, such as based on instructions from a control circuit. For example, the control circuit can be configured to select different equalizer circuit configurations when the equalizer circuit is used with signals transmitted via short and long cable lengths.
An adjustable equalizer circuit can thus be optimized for use with a particular transmission medium or input signal type.